The 2025 EarthSky Lunar Calendar is now available! Makes a great gift. Get yours today!<\/p>\n
New method for measuring black holes<\/h3>\n
If you were to watch a light flashing behind a black hole, a single flash might appear to you to repeat several times, like an echo. Why? Because massive objects like black holes warp the fabric of spacetime<\/em>. That means light rays from a single source can take multiple different curved paths around black holes. And so some should take longer than others to reach our eyes. A team of astrophysicists reported this month (November 7, 2024) that it has devised a technique for detecting and measuring these light echoes from the warped space around black holes. They said their new technique could help pierce the mystery of black holes, whose gravity is so powerful that light passing too close is forever captured. <\/p>\n Black holes don\u2019t emit light<\/em>. So scientists are always looking for innovative ways to measure black holes, and thereby learn more about them. This team says its new technique could help measure the size and rotation of black holes. Scholars from the Institute for Advanced Study in Princeton, New Jersey, led this new research. The peer-reviewed Astrophysical Journal Letters<\/em> published the new work on November 7, 2024. <\/p>\n Since the first evidence for Einstein\u2019s theory of general relativity in the year 1919, we\u2019ve understood that massive objects do literally bend spacetime. We\u2019ve known since then that when a light ray passes by an object with a huge gravitational pull, the path of the light will bend as it follows the curvature of space. <\/p>\n In more recent decades, astronomers have identified massive objects in space \u2013 including massive galaxies and giant black holes \u2013 that act as lenses. Such an object magnifies and distorts a light source located at a greater distance. Astronomers call the intervening objects gravitational lenses. <\/p>\n What\u2019s new here is the method for detecting and measuring light that\u2019s forced to travel multiple routes around an intervening black hole. George N. Wong is the study\u2019s lead author. He said:<\/p>\n That light circles around black holes, causing echoes, has been theorized for years. But such echoes have not yet been measured. Our method offers a blueprint for making these measurements, which could potentially revolutionize our understanding of black hole physics.<\/p>\n<\/blockquote>\n The scientists said they found a way to separate the faint light of individual echoes from the stronger light coming directly from matter circling the black hole. Their method relies on comparing the results of two very distant telescopes. It uses one on Earth and one in space, in a process called very long baseline interferometry. Very long baseline interferometry was the technique used to produce the first ever images of a black hole in 2019. That study used not just two, but multiple ground-based telescopes spread widely across Earth.<\/p>\n The team tested their technique by simulating tens of thousands of instances of light traveling around the supermassive black hole M87*. It\u2019s located 55 million light-years away at the center of the galaxy M87. <\/p>\n And eureka! They found their method was able to measure<\/em> how long the echoing photons were delayed before reaching an observer. <\/p>\n Importantly, the length of this echo delay is determined by both the mass and rotation of the black hole. And that\u2019s why this research could be great news for astrophysicists. Lia Medeiros, one of the study\u2019s authors, explained: <\/p>\n \nThis method will not only be able to confirm when light orbiting a black hole has been measured, but will also provide a new tool for measuring the black hole\u2019s fundamental properties.<\/p>\n<\/blockquote>\n We do have methods to calculate the spin and mass of black holes, but they\u2019re not entirely reliable. The accretion disk \u2013 the bright, spinning ring of material around the black hole \u2013 can interfere with these measurements. Being able to verify these values via light echo delays would give scientists far greater confidence when measuring the fundamental properties of black holes. <\/p>\n The echo detection method has not yet been tried outside simulations. But, according to the researchers, putting the plan into practice is well within current scientific capabilities.<\/p>\n Bottom line: Astronomers say they\u2019ve developed a new method to detect light that echoes around black holes. It could help them measure black holes\u2019 size and rotation.<\/p>\n Source: Measuring Black Hole Light Echoes with Very Long Baseline Interferometry<\/p>\n Via Institute for Advanced Study<\/p>\n Read more: What is gravitational lensing?<\/p>\n Read more: Milky Way\u2019s black hole in new image<\/p>\n <\/div>\n![\"A](\"https:\/\/earthsky.org\/upl\/2024\/11\/black-hole-light-echoes-wong-2024.png\")
Gravitational lensing around black holes<\/h3>\n
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How did they do it?<\/h3>\n
![\"Orange](\"https:\/\/earthsky.org\/upl\/2024\/03\/Black-hole-e1711544647397.jpg\")
Improving how we measure black holes<\/h3>\n
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